Towards Biomechanical Evaluation of a Transformative Additively Manufactured Flexible Pedicle Screw for Robotic Spinal Fixation

TL;DR

This paper introduces a novel flexible pedicle screw designed for improved biomechanical performance in spinal fixation, especially for osteoporotic patients, through additive manufacturing and experimental evaluation.

Contribution

It presents the design, additive manufacturing, and biomechanical testing of a flexible pedicle screw tailored for curved trajectories in spinal fixation.

Findings

Flexible screws show improved pullout strength in curved trajectories

Additive manufacturing enables complex screw geometries

Experimental results validate biomechanical advantages

Abstract

Vital for spinal fracture treatment, pedicle screw fixation is the gold standard for spinal fixation procedures. Nevertheless, due to the screw pullout and loosening issues, this surgery often fails to be effective for patients suffering from osteoporosis (i.e., having low bone mineral density). These failures can be attributed to the rigidity of existing drilling instruments and pedicle screws forcing clinicians to place these implants into the osteoporotic regions of the vertebral body. To address this critical issue, we have developed a steerable drilling robotic system and evaluated its performance in drilling various J- and U-shape trajectories. Complementary to this robotic system, in this paper, we propose design, additive manufacturing, and biomechanical evaluation of a transformative flexible pedicle screw (FPS) that can be placed in pre-drilled straight and curved trajectories. To evaluate the performance of the proposed flexible implant, we designed and fabricated two different types of FPSs using the direct metal laser sintering (DMLS) process. Utilizing our unique experimental setup and ASTM standards, we then performed various pullout experiments on these FPSs to evaluate and analyze their biomechanical performance implanted in straight trajectories.